The invention relates generally to electronic component packages, and more specifically, to a semiconductor package that is enhanced to reduce solder mask cracks and flakes.
1. Field of the Invention
This is a divisional application of Ser. No. 09/001,024, filed Dec. 30, 1997, that is currently pending. The invention relates generally to electronic component packages, and more specifically, to a semiconductor package that is enhanced to reduce solder mask cracks and flakes.
2. Description of Related Art
Electronic assemblies having components coupled to a printed circuit board (PCB) substrate, including plastic ball grid array (PBGA) devices, plastic pin grid array (PPGA) devices, etc., are well known in the art. The PCB substrates are processed as strips that are arranged to be separated, or singulated, into individual parts upon the completion of the assembly process.
FIG. 1 illustrates a prior art strip of PCB material 10. The prior art strip of PCB material 10 includes a plurality of segments 12, the boundaries of which are indicated by broken lines in FIG. 1. Each segment is adapted to receive one or more electronic components, such as a semiconductor die. When the assembly of the part is complete, the segments 12 are singulated into individual parts. Thus, during the singulation process, a singulation blade of a shear punch or router, for example, excises the individual segments 12 from the strip of PCB substrate into separate parts.
During the assembly of parts such as these, solder mask is typically applied over the entire surface of the substrate during the substrate manufacturing process. The solder mask functions to prevent solder from flowing to areas where solder is not desired. Moreover, solder mask provides a good adhesion surface to which a component, such as a semiconductor die, may be attached. Because the solder mask material is brittle, the singulation process may introduce cracks into the solder mask. Further, the singulation process often causes pieces of solder mask to flake off the singulation parts. FIG. 2 shows a prior art singulated assembly 14, illustrating an example of a crack 16 in the solder mask, and a solder mask flake 18 that has chipped off of the assembly 14 from a location 20.
The cracks 16 and flakes 18 cause several problems. For example, the crack 16 may result in a stress concentration, causing the crack 16 to propagate into the PCB material below, or into a conductive trace therein. This could bring about a functional failure of the assembly. Solder mask flakes 18 may cause problems in subsequent manufacturing operations. In particular, the solder mask flakes 18 may contaminate sockets of test equipment, requiring increased cleaning of the sockets to maintain production. Further, the solder mask flakes 18 may migrate to other areas of the package assembly facility, such as the area in which the semiconductor die is attached to the substrate, resulting in the die not being properly attached.
The present invention addresses some of the above mentioned and other problems of the prior art.
In one aspect of the invention, a substrate for a plurality of electronic assemblies, includes a strip of printed circuit board (PCB) material that includes a surface. The strip of PCB material includes a plurality of segments, with each segment adapted to receive at least one electronic component. The strip of PCB material is further arranged to be singulated into a plurality of individual electronic assemblies. Each segment has a perimeter portion located generally about the periphery of the segment, wherein the surface is covered with a solder mask, except for the perimeter portions.
In another aspect of the invention, a method of singulating a strip of PCB material into a plurality of individual substrate segments includes defining a plurality of perimeter portions about the periphery of each segment on a surface of the PCB material, and coating the surface with a solder mask, except for the perimeter portions. The substrate segments are singulated at the perimeter portions.